iPhone 8 Plus has intermittent WiFi connection

During my mom’s visit at my house, her iPhone 8 Plus had been experiencing a intermittent WiFi connection the whole time. Basically there’s network when she first connect to the router, and then after 10 minutes or so iOS will report there’s no internet connection. The AMPLIFI I have at home has firmware 2.9.3. I saw there are users complained about a similar problem with Apple devices about a year ago. I’m wondering whether there’s any known regression caused by firmware or specific iOS version or iPhone module that can explain this issue. Also any solution would be greatly appreciated!